Fasting of the month of Ramadan is a pillar of Islam. Muslim patients with chronic kidney disease (CKD) usually fast this month. To determine the effects of fasting on renal function in CKD patients, we prospectively studied 31 (19 males and mean age 54 ± 14.2 years) CKD patients during the month of Ramadan 1426 Hijra (4th October - 4th November 2005); 14 patients were in stage III CKD, 12 had stage IV and 5 had stage V. The mean estimated glomerular filtration rate (e-GFR) was 29 ± 16.3 mL/min. Diabetes was the main cause of CKD (19 (61%) patients), and hypertension was present in 22 (71%) patients. Clinical assessment and renal function tests were performed one month prior to fasting then during and a month later. Medications were taken in two divided doses at sunset (time of breaking the fast) and pre dawn (before starting the fast). All patients fasted the whole month of Ramadan with a good tolerance, tendency to weight reduction, and lower systolic and diastolic blood pressure. eGFR showed a significant improvement during the fast and the month after. The blood sugar was high during fasting with an increment in the Hb A1c. There was better lipid profile, reduction of the proteinuria and urinary sodium. We conclude that this study demonstrates a good tolerance and safety of fasting Ramadan in CKD patients.